1. Field of the Invention
The invention concerns a device for suspending one end of a saw blade.
2. Description of the Related Art
The term xe2x80x9cparallelogram-jigsawxe2x80x9d is basically intended to refer to any jig or fret saw in which a saw blade is secured or hung from the ends of two parallel arms pivoting in a parallelogram like manner. The saw blade holding ends of the arms are spread apart by a saw blade tensioner. They are limitedly flexible-elastic. Generally, one of the two arms is motor driven via a drive spindle, so that the saw blade moves back and forth in the longitudinal direction. In all known parallelogram saws and similar saws, the freeing of the upper saw blade end from the guiding arm, the subsequent insertion of the free end through a pre-borehole or an internal cutout in the work piece, and the subsequent securing of the saw blade back on the arm is relatively complicated and, with respect to the demands placed on the saw blade during sawing, is rather problematic. In some of the known saws, the saw blade clamps for securing the saw blade end may be easily accessible and operable, however they rigidly hold the saw blade ends or rigidly guide the same. Such saw blade clamps cannot exercise any pivoting movement with respect to the guide arm to which they are secured, whereby the saw blade breaks after a relatively short work time at its securing zone.
One known design of a parallelogram saw, which is produced by the company Hegner, VS-Schwenningen, Germany, is provided with a clamping device, which bears the logo xe2x80x9cSpecial saw blade clamp for internal cuts.xe2x80x9d This knife-edge shaped special clamp with frontal horizontally extending blade insertion slit and its blade securing point above its slit is pressed in the V-shaped receiving slit of the carrying parallelogram arm by means of a pressure screw situated above this clamp, whereby it remains completely rigid. So that any acceptable sawing process is even possible with this rigidly secured clamp, the stroke length of this parallelogram saw must be reduced. A non-blockage of this clamp would not be possible, since it would immediately tip or fold over under the high blade tension of the thin blade, since the blade securing point in this clamp is above its support slit. The saw blade naturally bends during each upward stroke below its securing point and breaks after a short period of time, usually already during idling. The sawing process is, besides this, very noisy. The cut is not clean and is imprecise, since the saw blade does not move correctly horizontally.
Further, the world wide known parallelogram-jigsaw of the Italian Company COLOMBO-FILLIPETTI for manufacturing of intarsia uses rigid saw blade clamps, which are rigidly screwed together.
In a second design of a known parallelogram saw, according to DE 2 334 911 C2, there is at the tip of the upper arm a knife edge or slit shape and free floating or pendulum saw blade clamp, which is supported by a receiving fork. Prior to each opening of the clamp, this must first be fixed or blocked using supplemental means, since it would otherwise fold or tip over. Besides this, the reintroduction of the upper blade and into the clamp slit frequently requires multiple attempts, since the fine slit in the receiving fork restricts the view onto the clamp. It is only by chance that the saw blade is correctly positioned in the clamp center.
A third design of a known parallelogram saw, namely the parallelogram-jigsaw well known in the United States of America and Canada under the name xe2x80x9cEXCALIBURxe2x80x9d from the company Tom Sommervile Design and Manufacturing, Inc., South Pickering, Ontario, Canada, with a saw blade clamp hung on the tip of the upper arm via a saw blade clamp hung for free and unlimited pendulum motion in the rotation axis, is on the one hand not restricted to the clamp slit, however during opening or closing of the clamp, this must first be held fast or blocked temporarily by some type of assisting device, for example a knock-out spindle, since otherwise a proper use thereof would not be possible. During closing of the clamp using a screw, the clamp easily turns in the rotation direction of the screw, and the blade can break. During opening, the clamp can pivot in the opposite direction, and the blade can threby also easily break. A further significant disadvantage of this design is comprised therein, that the clamp moves towards the back under the influence of medium-strong advance pressure of the work piece against the saw blade, whereby the saw blade deforms too strongly in a bow-like manner, and the cut surfaces at the work piece are convex or concave rather than being planar.
In accordance with the invention, a device is to be produced for suspending or securing one end of a saw blade on a first arm of a parallelogram-jigsaw or fret saw, which makes possible a substantially more rapid and secure mounting of the saw blade end on the arm, and at the same time, strongly reduces the risk of a break of the saw blade. At the same time, the device should guarantee a planar cut surface on the work piece.
The inventive device does not exhibit the above-discussed disadvantages of known devices of this type. In the inventive device, the saw blade end, preferably the upper saw blade end, is easily or lightly hung with free pendulum motion and can very rapidly and without problem, as well as without technical supplemental means or procedures, be secured again to the associated arm after release which makes possible the rapid, and production line like, carrying out of internal cut-outs.
In accordance with the invention a third arm forms a positive guide and runs freely along with the other two parallelogram arms. If the work piece during sawing suddenly produces a too high a pressure, then a counter force is produced at the pivot axis of the saw blade clamp. The saw blade clamp exerts then a pull force upon the limitedly elongatable third arm, which thereupon lengthens a slight amount. Usually it bows thereby simultaneously a small amount in the direction perpendicular to its longitudinal direction, the third arm which thus has become slightly longer makes it possible that the lower end of the saw blade clamp moves in a pendulum motion a bit towards the rear, that is, towards the rear side of the saw blade. The saw blade thereby forms a slight bow, whereupon however the upper saw blade end in the area just below the saw blade clamp remains completely straight, so that at this area it is not subjected to any amount of bending forces. It thus does not break. The third or force guidance arm continuously exerts a certain amount of a dampening effect with respect to the pressure exercised upon the saw blade clamp, which depends upon the changeable work piece advance rate.
If on the other hand during sawing suddenly a too high a pressure is exerted upon the saw blade back side, that is during turning or pulling of a work piece, then there is produced a pressure effect upon the third or positive guide arm, so that this is made somewhat shorter. The lower end of the saw blade clamp moves in a pendulum then a bit towards the front, whereby again the upper saw blade end in the area just below the saw blade clamp remains completely straight, and this does not suffer from any amount of bending forces and thus does not break. Here also the positive guide arm works as a dampener.
Particularly advantageous is the embodiment with an insertion slot for the saw blade accessible from below on the saw blade clamp. If one desires during the standby operation of the upper saw blade end for the purpose of manufacturing an internal cut out to free this from the saw blade clamp, it is sufficient to release the clamp screw. The clamp remains thereby in vertical orientation, since it is positively guided by a third arm, which does not lengthen or shorten, and since the torque on the screw exercises too small of an effect on the third arm. A temporary blockage of the saw blade clamp with supplemental means and a corresponding time loss can thus be dispensed with when using the inventive device. The clamp does not move forwards or towards the rear, either during opening or during closing thereof.
Various designs of the inventive third or positive guidance arm can be envisioned. Thus for example, a simple elongated rod of elastic material can be employed, or a non-elastic rod with only an a amount of elastic material for a pivoting mounting at the end of the third arm can be employed. A simple design can also be comprised therein, that both ends of a rod comprised of an only slightly elastic material and an upward or downward bend is provided, preferably both ends bent upwards or both downwards, so that doing pull or pressure load these bent ends can bend somewhat and thereby produce a slight yet effective elongation, or as the case may be, shortening of the arm. Also, multiple bends of the arm in different directions or spirals of the rod-shaped arm could provide minimal elongations or shortenings during pull or push forces against the arm. It is also possible to incorporate a piston-cylinder arrangement at an interruption point of the arm, whereby in the cylinder on both sides of the piston an elastic material can be employed, so that likewise doing pull or pressure load of the arm slight elongations or shortenings of the arm result in the longitudinal direction thereof.
In certain cases, the elasticity of the third arm can even be very small, whereby the pendulum motion of the saw blade cramp is quite limited, however on the basis of the already present play or tolerance of the rotation axis at both ends of the arm an effective elongation or shortening of the effective third arm can nevertheless occur and therewith a slight pendulum motion of the saw blade clamp can occur.
It is basically preferred to provide the third arm, in the case of vertical orientation of the parallelogram saw, above the first and second arms, which form the parallelogram. In principle, it is however possible to also provide the third arm at the lower side of the saw, that is below the saw table.